This invention relates in general to fluid treatment apparata and in particular to air treatment equipment for use in structures and in combination with air-circulating systems. In a variety of industrial equipment and residential systems, there is a need to filter or otherwise treat a recirculating medium such as, for example, air. Heating air associated with a forced air furnace is filtered so that the air which is emitted into the structure will be of a reduced particulate content. The quality of such circulating air may also be improved by the addition of moisture. A humidifier is typically employed for such treatment either as part of the furnace or by way of a separate apparatus.
Filtering arrangements are also employed with recirculating oil or coolant in machining centers, and similar filtering of either liquids or gases is found even when the fluid flow is not recirculating. In certain applications, such as the machining centers, the desire is prevent particles such as metal chips from damaging equipment. Yet in other applications, the desire is to remove contaminants such as dust, dirt, grease aerosols, etc. so that the emitted flow is clean and more healthful.
The type of filtering arrangement employed in such systems is a function of the size and type of particulate material to be removed, the resultant cleanliness desired, the amount of particulate material as a function of volumetric flow rate and the filter replacement philosophy. When filtering particles of extremely small size (less than one micron), the mesh or knit spacing of the filter must be quite small. This may be accomplished by laminating several filter layers of a random design or by a special type of single-thickness filter paper which is effectively a weave of several layers in a random knit pattern. One such special filtering paper is referred to as HEPA (High-efficiency particulate air) paper filter and has the capability of filtering submicron particles. There is, however, one disadvantage with such a material. This material can very quickly become "clogged" when particulate volume is heavy and once this occurs, the material is then no longer effective as a filtering means. HEPA paper is typically employed in a flat filter concept and once it becomes clogged, it is replaced due in part to the fact that before now, cleaning of such material was virtually impossible. Since the rate at which such a filter becomes clogged is directly related to the size of the filter and the volumetric flow rate of the substance being filtered and the particulate content, the length of time between filter changes could be lengthened by increasing the size of the filter and the cross-sectional area of the flow. While this is not possible when the filter is disposed across a fixed area inlet or outlet, it is possible to increase the length of time between filter changes by increasing the flow area and by arranging the filtering element into a continuous loop or belt and place it over a corresponding arrangement of rollers. By a zig-zag type weave of such a continuous belt, the total surface area exposed to the flow path is greatly increased over that of a flat filter. Further, it is possible to move the continuous belt past a cleaning station and extend the life of the continuous belt even more. This type of arrangement may be found in portable humidifiers where a belt arrangement is utilized to pick up moisture from a reservoir and pass it across an outlet at which time a fan blows through the filter to dispense moisture into the air.
One disadvantage with utilizing this concept of a continuous loop or belt arrangement with HEPA paper has been the inability to clean the paper and thus, the need to somewhat frequently replace this belt. Not only does such a belt represent a considerable expense, especially in view of the necessary arrangement of rollers, but there may be extensive time involved in the loading and unloading of replacement belts. However, these time and expense problems could be greatly minimized if the HEPA paper was able to be effectively cleaned. If HEPA material could be effectively cleansed while in place in the filtering device, then its life could be extended greatly and its overall desirability significantly increased. Since water is the most common medium for cleaning, its compatibility with HEPA material is critical. Once HEPA material becomes saturated with water or a water-based cleansing agent, it is thereafter unsuitable for further filtering. Consequently, if water or a water-based substance is to be used as part of the cleansing and/or humidifying system, it must be applied or utilized with respect to the HEPA material in such a manner that it will not result in saturation of the material.
Although HEPA material does have some degree of incompatibility with water, similar concerns must be considered if other types of filtering materials are utilized. The specific type of filter employed also becomes relevant with respect to the circulating medium that is going to be treated. While HEPA material may be preferred for submicronfiltering, different filter materials may be more desirable for humidifying applications or for other chemical treatment applications. If a continuous belt or similar carrier is used to retain and convey a particular liquid which is to be added to the circulating flow of air or other fluid, there first needs to be chemical compatibility. Secondly, if chemical residues may be left cleaning means are necessary to remove these residues so that the filtering element remains at full effectiveness. Other considerations involve mass flow rates and the amount of liquid to be added to the circulating medium. All of these factors are relevant in deciding what filtering element to use and how to use it.
The invention disclosed herein provides an improved air treatment apparatus capable of air filtering as well as optionally adding moisture to the air and chemical treatment of substances in the air. In one embodiment HEPA material is utilized as the filter means and cleaning means are provided to remove contaminants from this material and thereby greatly prolong the filter life.